The invention relates to a camshaft phaser or adjuster for the inner camshaft of a concentric camshaft assembly, and in particular to a camshaft phaser or adjuster for adjusting the relative rotational angle position of an inner camshaft of a concentric camshaft assembly relative to the phase position of the outer camshaft and the crankshaft of an internal combustion engine.
Camshaft phasers that operate according to the vane-cell principle for use on single camshafts are known. These are described in publications by the assignee of the present invention, including U.S. Pat. No. 6,805,080, which is incorporated herein by reference as if fully set forth. These work well in connection with DOHC engines where all the intake or exhaust cam lobes are located on separately located intake and exhaust camshafts.
It has also been known to use camshaft phasers in connection with concentric camshaft assemblies for controlling the phase position of the inner camshaft, the outer camshaft or both. One such arrangement is described in DE 10 2006 024 793 A1. This publication discloses a dual phasing system for a concentric camshaft assembly which includes two camshaft phasers which are located at the front of an engine that are axially spaced adjacent to one another. These two camshaft phasers allow independent control the rotation angle of the outer and inner co-axial camshafts relative to the crankshaft in order to allow separate adjustment of the timing of the intake and the exhaust valves of the internal combustion engine. However, this arrangement provides additional complexity which is often not required to obtain many of the benefits of adjusting either the inner or the outer camshafts of a concentric camshaft assembly without the need for adjusting both.
A problem with the known camshaft phasers for use with either or both the inner and outer camshafts of a concentric camshaft assembly is that the chain or belt loads from the timing chain or belt are transmitted to the inner camshaft. This can cause bending and binding of the inner camshaft relative to the tubular outer camshaft. Additionally, in the prior known systems, the phaser is formed with opposing vanes extending from the front and rear covers of the phaser, toward one another, with one of the covers being attached to the inner shaft and the other cover being attached to the outer shaft. This arrangement has been shown to lack durability and includes basic design flaws which affect the functionality of such proposed systems.
It would be desirable to provide a camshaft phaser for a concentric camshaft assembly that allows for phasing of either the intake or exhaust lobes of a camshaft in which the drive load from the timing chain or belt extending from the crankshaft to the timing gear or timing belt pulley of the concentric camshaft arrangement is transmitted to the outer shaft of the concentric camshaft. Additionally, it would be desirable to provide the phaser as a preassembled unit which can be installed in a simple manner during assembly of the engine, minimizing the complexity of the assembly steps required. Further, the phaser should be removable as a single unit for service so that it can be easily removed and installed in the field.